A duplex communication system includes two connected transceivers that communicate with each other in both directions. There are two types of duplex communication systems: full-duplex communication systems and half-duplex communication systems. In full-duplex communication systems, the two connected transceivers communicate with each other simultaneously, in both directions. In half-duplex communication systems, the two connected transceivers communicate with each other in one direction at a time; that is, only one of the two transceivers transmits at any given point in time while the other receives.
Cellular communication networks are often half-duplex (or at least capable of operating in a half-duplex mode) as specified by the network technologies that they employ. For example, common half-duplex, cellular network technologies include Worldwide Interoperability for Microwave Access (WiMAX) operating in a Time Division Duplexing (TDD) mode and Long-Term Evolution (LTE) similarly operating in a TDD mode. TDD is the application of time-division multiplexing to separate incoming and outgoing signals and is used by WiMAX and LTE to emulate full-duplex communication over a half-duplex communication link. WiMAX is specified by the IEEE 802.16 standard, and LTE is specified by standards developed by the 3rd Generation Partnership Project (3GPP).
FIG. 1 illustrates an exemplary half-duplex cellular communication network 100, such as a WiMAX or LTE-TDD cellular communication network, distributed over land areas 110A-C called cells, each of which is served by a base station 120. Cells 100A-C are joined together to enable various user equipments (UEs) 130 (e.g., mobile phones, laptops, personal digital assistants, pagers, etc.) to transmit data to and receive data from a network (not shown) via base stations 120 over a wide geographical area.
Because cellular communication network 100 is half-duplex, UEs 130 cannot transmit data to the network via base stations 120 at the same time as they are receiving data from the network via base stations 120. This half-duplex limitation is typically the result of uplink transmissions (i.e., transmissions from UEs 130 to base stations 120) sharing the same carrier frequency or channel as downlink transmissions (i.e., transmissions from base stations 120 to UEs 130). For example, in both WiMAX and LTE-TDD there is only a single carrier frequency and uplink and downlink transmissions in a cell are separated in time.
One issue in half-duplex cellular communication networks, such as half-duplex cellular communication network 100, is potential interference from other cellular communication networks deployed in the same geographical area. In particular, when two half-duplex cellular communication networks are deployed in the same geographical area and operate over adjacent carriers (i.e., carriers next to each other in frequency), the two networks can substantially interfere with each other. The majority of the interference between the two half-duplex cellular communication networks occurs as a result of uplink transmissions from one of the two networks overlapping with downlink transmissions from the other network, and vice-versa.
Therefore, what is needed is a method and system for mitigating the interference between two half-duplex cellular communication systems operating over adjacent carriers in the same geographical area.
The present invention will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.